The different faces of renal angiomyolipomas on radiologic imaging: a pictorial review.

Br J Radiol. 2018 Apr; 91(1084): 20170533. Published online 2018 Feb 6. doi: 10.1259/bjr.20170533 PMCID: PMC5965995 PMID: 29327940 The different faces of renal angiomyolipomas on radiologic imaging: a pictorial review Shanigarn Thiravit, MD,1 Wanwarang Teerasamit, MD,1 and Phakphoom Thiravit, MD1 Shanigarn Thiravit 1Department of Radiology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand Find articles by Shanigarn Thiravit Wanwarang Teerasamit 1Department of Radiology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand Find articles by Wanwarang Teerasamit Phakphoom Thiravit 1Department of Radiology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand Find articles by Phakphoom Thiravit Author information Article notes Copyright and License information Disclaimer 1Department of Radiology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand Corresponding author. Shanigarn Thiravit: ; Wanwarang Teerasamit: moc.liamg@pmaijom; Phakphoom Thiravit: Address correspondence to: Dr Shanigarn Thiravit. E-mail: Received 2017 Jul 17; Revised 2017 Dec 19; Revised 2017 Nov 12; Accepted 2018 Jan 9. Copyright © 2018 The Authors. Published by the British Institute of Radiology Abstract Renal angiomyolipoma (AML) is an uncommon renal tumour, generally composed of mature adipose tissue, dysmorphic blood vessels and smooth muscle. Identification of intratumoral fat on unenhanced CT images is the most reliable finding for establishing the diagnosis of renal AML. However, AMLs sometimes exhibit atypical findings, including cystic as well as solid forms; some of these variants overlap with the appearance of other renal tumours. A rare type of AML, the epithelioid type, possesses malignant potential. The aim of this pictorial review is to gather the different imaging features of AMLs including the classic and fat-poor types, AMLs with epithelial cysts, epithelioid AML, AML associated with tuberous sclerosis, haemorrhagic AML and large AMLs mimicking retroperitoneal liposarcomas. The diagnostic clues that help to distinguish AMLs from other renal tumours are also described in the review. Introduction Renal angiomyolipoma (AML) is an uncommon renal tumour, usually discovered incidentally on diagnostic imaging. Renal AMLs occur more in females than in males.1 About 80% of renal AMLs are sporadic, usually occurring in the fifth decade. The other 20% are associated with tuberous sclerosis complex (TSC) and occur in a younger age group, usually the third decade.2 AML is also associated with lymphangiomyomatosis.1 Once considered a benign renal hamartoma, renal AML has been recognized as part of the family of perivascular epithelioid cell tumours (PEComas), that express myogenic (human melanosome B [HMB]−45) and melanocytic (actin and/or desmin) markers.1 The PEComas also relate to TSC due to losses of TSC1 or TSC2 genes that may have a role in the regulation of the mammalian target of rapamycin) pathway.2 Renal AMLs are triphasic tumours, composed of mature adipose tissue, dysmorphic blood vessels, and smooth muscle in varying proportions, which contribute to the imaging characteristics. AMLs sometimes present with atypical findings and may mimic renal cell carcinoma (RCC). Recently, two radiologic classifications of renal AMLs have been introduced. Jinzaki et al categorized them into classic and fat -poor subtypes, and another classification by Song et al categorized them into fat-rich, fat-poor, and fat-invisible subtypes.1, 3 In this pictorial review, CT and MRI features of classic and fat-poor AMLs, AMLs with epithelial cysts (AMLEC), and epithelioid AML (EAML) are summarized (Table 1) and the other different imaging features of AMLs including AMLs associated with tuberous sclerosis, haemorrhagic AML, and large AMLs mimicking retroperitoneal liposarcomas are also described. It is important for radiologists to familiarize themselves with the spectrum of AML morphology to be able to establish the correct diagnosis and help clinicians with further treatment planning. Table 1. CT and MRI features of angiomyolipomas Types of AMLs CT MRI Classic UE: Fat attenuation (<–10 HU) FS: Signal drop No calcification CS: India-ink artefact at macroscopic fat-water interfaces CE: ± Intratumoral aneurysm T2W: Hyperintense area corresponding with signal drop out on fat-suppression image secondary to macroscopic fat Hyperattenuating fat-poor UE: Hyperdense (usually > 45 HU) FS: No signal drop No fat attenuation CS: No signal drop No calcification T2W: Homogeneous hypointense No cystic/Necrotic change CE: Variable, frequently homogeneous early enhancement with subsequent washout Isoattenuating fat-poor UE: Isodense (between –10 HU and 45 HU) FS: No signal drop No fat attenuation CS: Signal drop on OP compared with IP No calcification T2W: Hypointense No cystic/necrotic change CE: Variable, ± gradually progressive enhancement AML with epithelial cyst UE: Solid part; hyperdense (usually > 45 HU) FS: No signal drop Cystic part; isodensity CS: Solid part; ± signal drop on OP compared with IP. CE: Solid part; ± homogeneous early enhancement with subsequent washout T2W: Solid part; Hypointense Cystic part; ± multiloculated, no enhancement Cystic part; Bright signal Epithelioid UE: ± Fat attenuation FS: ± Signal drop ± Calcification CS: ± Signal drop on OP compared with IP. ± Internal haemorrhage, Necrosis T2W: Heterogeneous hypointense CE: Heterogeneous ± Hyperintense from necrosis Variable enhancement Presence of vascular invasion Presence of metastasis Open in a separate window AML, angiomyolipoma; CE, contrast enhanced CT; CS, chemical shift MR image; FS, fat suppression MR image; HU, Hounsfield unit; IP, in phase image; OP, opposed phase image; T2W, T2 weighted MR image; UE, unenhanced CT. Imaging findings in angiomyolipomas Classic AML On ultrasound, AMLs are typically highly hyperechoic, equal to the echogenicity of renal sinus fat. RCCs and oncocytomas tend to display echogenicity hyperechoic to the renal cortex but less than the echogenicity of renal sinus fat (Figure 1).4 Despite specific findings that have been described, e.g. posterior shadowing for AMLs, and a hypoechoic rim and internal cysts for RCCs, all echogenic renal lesions should undergo CT for further evaluation.4 On CT, visible fat density is a hallmark, appearing as an internal hypodense area with attenuation <−10 HU on unenhanced CT (UECT) images.1 It is important to use thin CT sections (1.5–3 mm) to detect small amounts of fat (Figure 2).1 Although rare, RCCs may contain macroscopic fat from perinephric fat engulfment, lipid-producing necrosis, or osseous metaplasia.5 Atypical oncocytomas with perinephric fat extension can also present as a fat-containing renal mass.6 Distinguishing AMLs from o (...truncated)